If we consider Life as a whole, what are the best and worst possible outcomes for it? How would Life rank these foreseeable outcomes? I understand the primary aim of Life to be survival and propagation. So from this, the simplest ordering would be:

1) Life continues to exist
2) Life dies

We can add nuance to this in several ways. The first consideration, is to recognize that Earth will eventually become inhospitable to Life, either through man-made or astronomical disaster. Given this, we can update our ordering:

1) Life proliferates to other planets
2) Life continues on Earth until Earth becomes inhospitable to Life, and then dies
3) Life dies before Earth becomes inhospitable to Life

From the perspective of Life 2) and 3) are equivalent, just on a different timeline. So this ordering can be simplified to:

1) Life proliferates to other planets
2) Life dies on Earth

The next level of nuance is whether or not Life could begin anew if it completely died out on Earth. If it could not begin anew, the above ordering is not changed, but if abiogenesis could take place again on earth, they we may have the following ordering:

1) Life proliferates to other planets
2) Life dies on Earth, emerges again, and this new Life proliferates to other planets
3) Life dies on Earth, emerges again, and again, but never proliferates to other planets
4) Life dies on Earth, and does not emerge again

This ordering brings up an interesting question: How much do we care about our specific instance of Life vs other iterations of earth-originating life (let's call Life2)? It seems reasonable that we care about Life (of our specific lineage) more than Life2. For example, how would Life2 be different than mars-originating (or any other alien) beings? I experience this question as one without an intuitive answer. Humans have no experience with living beings that are not part of Life, so it is difficult to intuit their moral worth to us. For the sake of this Life-centered argument, I will argue that future re-emergences of life (such as Life2) bear no value to Life, which means 2) 3) and 4) have the same value, as it results in the death of Life. This again leaves us with the ordering of outcomes;

1) Life proliferates to other planets
2) Life dies on Earth

The next aspect to consider is the role that humans can play in this goal. We are currently the only species capable of intentional space exploration. Given this, it is understandable that most current efforts are to send humans to other planets. This seems like a straightforward strategy: as we are the beings that have developed spaceflight, we should be the first to live on new planets. This approach assumes the following ordering of outcomes:

1) Humans poliferates to other planets
2) Life dies on Earth

But we can see that this ordering makes an oversight. There are ways for Life to be spread to other planets. For example, probes with genetically engineered microbes could be sent to Life-sustaining planets in order to germinate there. But which strategy would best serve Life? Should we try to establish a sustainable off-world colony of humans, or begin sending Life-colonizing probes through our galaxy? This decision hinges on several probabilities that we do not have a good understanding of:

- Probability of intelligence re-emerging from simpler lifeforms
- Probability of humans becoming self-sustaining on non-earth planets
- Probability of Life becoming self-sustaining on non-earth planets
- Probability of humanity destroying itself on Earth

Given these unknowns, the best approach would be to try both strategies at the same time: we should try to establish sustainable human colonies, as well as send Life probes to more distant planets. These strategies are not in competition, and some technologies or breakthroughs in one strategy may benefit the other.